## Seminars and Colloquia by Series

Monday, August 14, 2017 - 14:11 , Location: Skiles 006 , Albert Fathi , Georgia Tech , Organizer: Dan Margalit
We will give different topological very simple statements that seem not to have been noticed, although they are of the level of Brouwer’s fixed point theorem. The main result is: Let F be a compact subset of the manifold M. Assume g:F->M is a continuous map which is the identity on the boundary (or frontier) of F, then the image g(F) contains either F or M\F.
Monday, August 7, 2017 - 14:05 , Location: Skiles Conference Room 114 , Ingrid Irmer , University of Melbourne , Organizer: Stavros Garoufalidis
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Wednesday, July 19, 2017 - 14:16 , Location: None , None , None , Organizer: Dan Margalit
Friday, July 7, 2017 - 10:30 , Location: Skiles 006 , , Michigan , Organizer: Justin Lanier
There has been a recent interest in studying surfaces of infinite type, i.e. surfaces with infinitely-generated fundamental groups. In this talk, we will focus on their mapping class groups, often called big mapping class groups. In contrast to the finite-type case, there are many open questions regarding the basic algebraic and topological properties of big mapping class groups. I will discuss several such questions and provide some answers. In particular, I will discuss automorphism groups of mapping class groups as well as relations between topological invariants of a surface and algebraic invariants of its mapping class group.  The results in the talk are based on recent joint work with Priyam Patel and ongoing joint work with Javier Aramayona and Priyam Patel.
Tuesday, June 27, 2017 - 14:05 , Location: Skiles 006 , Lei Chen , University of Chicago , Organizer: Dan Margalit
I will talk about homomorphisms between surface braid groups. Firstly, we will see that any surjective homomorphism from PB_n(S) to PB_m(S) factors through a forgetful map. Secondly, we will compute the automorphism group of PB_n(S). It turns out to be the mapping class group when n>1.
Friday, June 23, 2017 - 10:00 , Location: Skiles 006 , , Temple University , , Organizer: Justin Lanier
Certain fibered hyperbolic 3-manifolds admit a layered veering triangulation, which can be constructed algorithmically given the stable lamination of the monodromy. These triangulations were introduced by Agol in 2011, and have been further studied by several others in the years since. We present experimental results which shed light on the combinatorial structure of veering triangulations, and its relation to certain topological invariants of the underlying manifold. We will begin by discussing essential background material, including hyperbolic manifolds and ideal triangulations, and more particularly fibered hyperbolic manifolds and the construction of the veering triangulation.
Tuesday, June 20, 2017 - 14:05 , Location: Skiles 006 , Dan Margalit and Justin Lanier , Georgia Tech , Organizer: Justin Lanier
We give a simple geometric criterion for an element to normally generate the mapping class group of a surface. As an application of this criterion, we show that when a surface has genus at least 3, every periodic mapping class except for the hyperelliptic involution normally generates. We also give examples of pseudo-Anosov elements that normally generate when genus is at least 2, answering a question of D. Long.
Monday, May 8, 2017 - 14:00 , Location: Skiles 006 , Tye Lidman , NCSU , Organizer: Jennifer Hom
We will discuss a relation between some notions in three-dimensional topology and four-dimensional aspects of knot theory.
Monday, April 24, 2017 - 14:30 , Location: UGA Room 303 , Alexandru Oancea and Basak Gurel , Jussieu and University of Central Florida , Organizer: Caitlin Leverson
Alexandru Oancea: Title: Symplectic homology for cobordisms Abstract: Symplectic homology for a Liouville cobordism - possibly filled at the negative end - generalizes simultaneously the symplectic homology of Liouville domains and the Rabinowitz-Floer homology of their boundaries. I will explain its definition, some of its properties, and give a sample application which shows how it can be used in order to obstruct cobordisms between contact manifolds. Based on joint work with Kai Cieliebak and Peter Albers. Basak Gürel: Title: From Lusternik-Schnirelmann theory to Conley conjecture Abstract: In this talk I will discuss a recent result showing that whenever a closed symplectic manifold admits a Hamiltonian diffeomorphism with finitely many simple periodic orbits, the manifold has a spherical homology class of degree two with positive symplectic area and positive integral of the first Chern class. This theorem encompasses all known cases of the Conley conjecture (symplectic CY and negative monotone manifolds) and also some new ones (e.g., weakly exact symplectic manifolds with non-vanishing first Chern class). The proof hinges on a general Lusternik–Schnirelmann type result that, under some natural additional conditions, the sequence of mean spectral invariants for the iterations of a Hamiltonian diffeomorphism never stabilizes. Based on joint work with Viktor Ginzburg.
Monday, April 17, 2017 - 14:05 , Location: Skiles 006 , Chaohui Zhang , Morehouse College , Organizer: Dan Margalit
Let S be a Riemann surface of type (p,1), p > 1.  Let f be a point-pushing pseudo-Anosov map of S.  Let t(f) denote the translation length of f on the curve complex for S.  According to Masur-Minsky, t(f) has a uniform positive lower bound c_p that only depends on the genus p.Let F be the subgroup of the mapping class group of S consisting of point-pushing mapping classes.  Denote by L(F) the infimum of t(f) for f in F pseudo-Anosov.  We know that L(F) is it least c_p.  In this talk we improve this result by establishing the inequalities .8 <= L(F) <= 1 for every genus p > 1.